Typewriter or printer ribbons with separate inked strips are known. For example, German Offenlegungsschrift 1,436,756 discloses a ribbon with one inked strip for regular printing and another strip with correcting ink for covering mistakes.
Most conventional typewriter or printer ribbons are made of nylon. The nylon ribbon acts as a carrier for a colored liquid (usually an oil and ink mixture) which is absorbed by the fibers of the nylon. When the nylon impregnated with the colored liquid is hit by the pins of a print head on a dot matrix printer, or the print head of a conventional printer or typewriter, the colored liquid is forced out of the ribbon and transferred onto the paper being printed.
Following the transfer of the colored liquid onto paper, remaining colored liquid flows out of the surrounding areas back into the used zone to regenerate the typewriter or printer ribbon. Such conventional ribbons have colored liquid on both sides of the ribbon, so that the pins or types of the print heads, necesarilly, come into contact with the colored liquid. This contact limits the technical possibilities for the design of the print head because of the abrasive and caustic nature of conventional colored liquids; or, alternatively, the selection range of colored liquids that can be used is limited to the type of print head used.
Conventional coloring agents in colored liquids are either insoluble pigments or soluble dyes. Pigments are superior to dyes in both color yield and light stability, however, pigments are much more abrasive than dissolved dyes. Because of the superior quality of pigments in printing, the industry would use it preferrably over dyes if the abrasive effects of pigments on pin heads could be overcome. For instance, despite the fact that pigments cause serious abrasion and wear problems on printer heads and pins, pigments are, nevertheless, used by the industry on ribbons.
Present methods of attentuating the abrasive effects caused by pin heads coming into contact with pigments include having, as a general rule, less than 10% pigment in the colored liquid. Even with less than 10% pigment, it is still necessary to use expensive abrasion-resistant materials and lubricant systems for the print head construction to avoid the accelerated wear caused by print heads coming into contact with pigments during printing. Thus, there is a need in the industry for ribbon which are designed such that superior print quality pigments can be used while, simultaneously, preventing excessive wear of type or pin heads.
Backing films are sometimes used in typewriter or printer ribbons and have certain advantages over nylon. In conventional ribbons with backing film, the colored liquid is coated onto support film. When insoluble pigments are used in the colored liquid coating, the film can act as a buffer layer shielding the print head from the pigments. The film can be constructed in such a manner that the pins never penetrate the support film, and, thus, would not come into contact with the coating. With such construction, abrasion on print heads is caused only by ordinary wear and tear caused by constant contact of the printhead with the support film.
However, the trade-off in using backing film instead of nylon is the limited use obtained from a roll of coated film. Unlike nylon which can regenerate used zones as described above, the coated film can only be used for one linear pass-through and its surface cannot be regenerated in the form of a continueing loop. Thus, the confines of the internal space of a typewriter or printer limit the amount of backing film that can be placed into a ribbon cassette or cartridge. The user of such designs is constantly replacing spent cassettes leading to poor economic efficiency in terms of man-hours and the cost of constant replacement.
It is, therefore, an object of the present invention to provide a typewriter or printer ribbon with superior color yield while preventing excessive wear of pin or type heads caused by abrasive pigments, and, further, provide extended duration of use before discarding and replacement.
To this end, the present invention incorporates onto support film, inked strips disposed alternately offset with respect to one another at equal intervals on the front and back of the support film and perpendicular to the longitudinal direction of the support film so that the "back" of the support film, which is opposite the coated side, has no ink. Furthermore, a Moebius loop is utilized and the ends of the ribbon are joined into a continous loop by means of conventional adhesive strips in a manner which doubles the useful life of the ribbon of the present invention.